[Form] fix form handling with unconventional request methods like OPTIONS
bug #12170 [Form] fix form handling with OPTIONS request method (Tobion)

This PR was merged into the 2.3 branch.

Discussion
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[Form] fix form handling with OPTIONS request method

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8282
| License       | MIT
| Doc PR        | -

The OPTIONS request is just handled as any other request method. And accoring to the spec, an options request can also contain a request body like a POST. This only applied when using the deprecated form processing with `$form->submit($request)`. The change also makes the handling consistent with the `handleRequest` behavior via https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Form/Extension/HttpFoundation/HttpFoundationRequestHandler.php

Commits
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28eabd8 [Form] fix form handling with unconventional request methods like OPTIONS